1. Field of the Invention
The present invention relates generally to a method for cleaning an EGR cooler of an exhaust gas recirculation system, and more particularly to a method for cleaning an EGR cooler of an exhaust gas recirculation system that intentionally creates condensation within the EGR cooler to effectively reduce particulate buildup.
2. Background
The demand for cleaner burning internal combustion engines has continued to increase in recent years. This is largely due to the fact that internal combustion engines generally do not completely burn fuel, and in any event produce various by-products in the emitted exhaust that can be harmful to the environment. Common by-products typically include nitrous oxides, carbon monoxide, carbon dioxide, and various hydrocarbons. These by-products not only pose harm to the environment, but some represent wastefulness in that they have not been fully burned. These by-products, particularly the solid particulate matter commonly referred to as soot, can accumulate in associated systems through which they pass. Methods to simply remove these by-products have included traps of various designs, as well as filter arrangements. While methods to further burn these by-products and thus increase the level of combustion efficiency include passing the exhaust gas through afterburners, in more recent years, recirculation of at least a portion of the exhaust gas back into the air intake of the engine has been implemented and the arrangements that accomplish this recirculation are typically referred to as exhaust gas recirculation systems, or EGR system for short. The present invention is directed to such an EGR system.
An EGR system recirculates a portion of exhaust gas back into the intake of a combustion engine. This recirculation not only allows for further combustion of the exhaust by-products, but it also selectively advantageously dilutes the incoming fuel charge in the cylinders. Temperature adjustments to the combustion mixture can also be affected using the EGR system, including lowering combustion temperature which reduces certain emissions, such as nitrous oxide. To achieve a lower temperature in the otherwise high-temperature exhaust gas, the recirculated exhaust gas is typically cooled before being introduced to the intake of the engine thereby effectively lowering the ensuing combustion temperature. This process is generally accomplished through an EGR cooler. When the exhaust gas is passed through the EGR cooler, the particulate matter can adhere to the EGR cooler where it compacts and hardens over time. This accumulation reduces the cooling efficiency of the EGR cooler as the particulate accumulation effectively insulates the coolant coils, inhibiting the coolant coils from cooling the exhaust gas. From a structural perspective, the EGR cooler is interiorly configured basically as a radiator with cooling coils located therein, and through which reduced-temperature coolant is circulated. If the particulate accumulation is not addressed, it not only leads to potentially damagingly high temperatures in, and after the EGR cooler, but the restriction that the build-up poses also inhibits flow of exhaust gas being recirculated therethrough, and can even effectively cause a blockage at the EGR cooler in extreme cases. This buildup effectively shortens the service life of the EGR system, necessitating frequent and expensive cleaning of the EGR cooler to promote efficiency and prevent excessive fouling of the exhaust gas recirculation flow path. Thus a method to prevent, or at least reduce accumulation of this particulate residue in an EGR is desired.
Several methods have been developed to address the particulate accumulation problem. One such method is to simply place a filter upstream of the EGR cooler. This effectively traps a certain amount of hydrocarbon particles before they enter the EGR cooler. Such a filter is described in U.S. Pat. No. 6,474,319, issued to Hough et al. and entitled Filter System For The Removal Of Hydrocarbon Deposits From A Cooled Exhaust Gas Recirculating Engine. Such a filter system, however, not only requires the additional cost of a filter that further requires cleaning and maintenance, but also typically necessitates the use of a catalyst and/or heating means to reduce the build up of particles that inevitably occur at the filter.
Another similar method implements a carbon filter, but places a non-thermal plasma generator upstream of the filter to oxidize carbon deposited, or trapped on the filter. Such a method is disclosed in U.S. Pat. No. 6,474,060, issued to Khair and entitled Exhaust Gas Recirculation Filtration System. Again, although this method will reduce the amount of particulates entering into the EGR cooler, it still requires additional parts leading to increased expense and maintenance, and ultimately, build-up in the EGR cooler can occur.
Another attempt to alleviate the problem of particulate buildup uses a protective coating that when applied to the components of the EGR system reduces the tendency of particles to adhere to the coated region and may also reduce the risk of sulfuric acid corrosion. A protective, prophylactic coating is disclosed in PCT Publication No. WO 02/099261 entitled Protective Coating For Internal Combustion Engine Components. While this method may indeed reduce the buildup of hydrocarbons, it is unclear as to whether this coating will continue to do so after an extended length of time operating under the corrosive environment caused by hard-working diesel engines.
A well-known concern for the industry is preventing condensation from occurring within EGR systems. This is of particular concern at the EGR cooler where temperature lowering is purposely caused to the exhaust gas; and therefore, special care has been traditionally taken to assure that no condensation-forming conditions are permitted at the EGR cooler. This is largely due to the fact that fuels, for instance diesel fuel, contain a certain level of sulfur. When this sulfur combines with water resulting from condensation or otherwise, corrosive sulfuric acid is produced.
The present invention provides a solution to the problem of hydrocarbon particle buildup in an EGR cooler 18 of a standard EGR system without adding additional parts, cost and maintenance concerns, and it provides a solution that should endure over a typical life span of an internal combustion engine. Still further, the teachings of the present invention are based on tenets diametrically opposed and counter to traditional thinking within the EGR-utilizing industries, and therefore constitute and deliver surprising results.